Electric induction furnace



March 29, 1932. GREENE 1,851,575

ELECTRIC INDUCTION FURNACE Filed Dec. 5, 1928 2 Sheets-Sheet l March 29,1932. GREENE 1,851,575

ELECTRIC INDUCTION FURNACE Filed Dec. 3, 1928 2 Sheets-Sheet 2 Fig.3. il H IQIFLJKEST/LFELW' u iii-5 J II J O 37 INVENTOR Patented Mar. 29,1932 PATENT OFFICE ALBERT E. GREENE, OF MEDINA, WASHINGTON ELECTRICINDUCTION FURNACE Application filed December 3, 1928.

to an imoperation My present invention relates provement in inductionfurnace and apparatus therefor.

Induction furnaces prior to my invention described in this applicationwere not suited for melting cold loose metal scrap. They did not providesufficient voltage in the molten metal secondary circuit to overcome thecontact resistance between loose pieces of scrap metal charged into thechannel without molten metal to complete a circuit all around thechannel. They operated at comparatively low single turn voltages ofaround 5 to 10 volts and at high amperages. These earlier furnaces werestarted by placing a solid ring of metal in the channel of the furnaceand slowly and carefully heating it until it finally melted. Often thering would crack or melt at one place and the voltage would beinsuflicient to cause the current to continue to flow. would then haveto be put in. Sometimes these furnaces were started by pouring moltenmetal into the secondary channel and heating this by the low inducedvoltage current. Thus it was not possible, prior to my discoverydescribed herein, to throw loose scrap such as steel punchings into achamber of an induction furnace and cause current to flow thru thesecondary circuit including this loose scrap and melt it.

In the type of induction furnaces at present known to the art wherein anannular channel for receiving the metal charge forms a secondary circuitand is surrounded by an induction coil connected in the primary circuit,as the channel becomes filled with metal and the current increased byreason of the decreased resistance in the secondary circuit the powerfactor becomes so low that further increase in the usual low voltageresults only in increasing the current out of phase with the voltagewithout increasing the heat generated within the channel. Thisdifiiculty my invention proposes to overcome by providing passages ofrelatively small cross-section in the annular channel where the channeltraverses the field of the primary circuit and increasing the voltage inthis secondary circuit. This results in the at- A new ring l Serial No.323,515.

tainment of a high arcing between the the cold of the furnace withoutthe preliminary introduction of a quantity of molten metal or a solidmetal ring to initially provide a closed secondary circuit.

y invention has for one of its provisions the overcoming of the pincheffect which tends to rupture the flow of molten metal when subjected tohigh current densities.

y inducing a relatively high arcing voltage in the secondary circuitcomposed of the metal charge any tendency of the circuit to beinterrupted by reason of pinching off of the molten metal stream isavoided by the formation of an arc across the rupture.

The induction of current may be by means primary winding arcing voltagesin a single turn circuit around a magnetic core. These single turnvoltages may be as high as 300 volts or more, but in small furnaces Iutilize voltages of from 20 to 50 volts in the single turn secondarycircuit to advantages.

have discovered that by utilizing the relatively high voltages describedherein in a single turn induction furnace secondary circuit, that incertain forms of my invention I secure improved operation by includingone or more electrodes in the circuit and I may operate so that theseelectrodes form part of the single turn secondary circuit, or I may anddo in certain cases utilize these electrodes to supply separate currentto the charge.

In the operation of my furnace where it is rocked, I have discovered asimple means of combining a rocking and a tilting mechanism with thesame apparatus. I have discovered a combination in which I use a tiltingcylinder mounted on the foundation so as to allow for movement about ashaft at the base of the cylinder and having a piston rod which servesto connect to and tilt the furnace over, and furthermore, by providing asmall cylinder on the furnace end of the rod,

vide means for more extended lead, and in this form of my invention Iapply relatively higher voltages thru secondary circuits includingresistor elements forming part of the circuit. Thus, in meltingaluminum, where the lightness of the metal results in bubbling up,-asort of modified pinch effect-I use a hollow tube, for example graphite,forming part of the single turn secondary circuit, and so proportion theresistance of this tube in relation to that of the metal passing thru itas to avoid the bubbling and add the necessary heat to the aluminum. Inmelting such metals, and especially zinc and lead, I may use a metalcontainer forming part of the secondary circuit and containing themolten metal. Thus as a galvanizing pot I may use two main chambers ofsteel connected by relatively small tubes of steel or iron andencircling magnetic cores, so as to induce current in both the tube andin the metal contained in it; and I may use the container as thepreliminary heating element to start the operation before the containedzinc or other metal is melted inside it.

My invention is not limited to the melting of scrap metal for I havediscovered that by the method and means of my present invention orecharges and other materials may be advantageously heated and melted andtreated. I have also discovered that by means of a high E. M. F. of themagnitude required inarc furnace circuits, I may advantageously applyelectric heat for melting cold charge in a melting chamber whereby thisrelatively high E. M. F. is utilized between the ends of the moltenmetal portion of the single turn secondary to heat the charge in thatlocation. In this form of my invention there are 'a number of importantfeatures, including the use of a sloping hearth to limit the completionof the molten metal circuit clear around the core and the provision forwater cooling of the hearth portion which slopes or which forms anelevated part or bridge between the ends of the molten metal part of thesecondary. The transformer design provides means for limiting shortcircuit currents thru the metal in case they occur, by the reactanceeffect. Electrodes also may be used, either as part of the single turnsecondary circuit or independently, or not at all. It is the ability toprovide a relatively high E. M. F. in this circuit which makes possiblethe improvements I have disclosed.

The use of a high E. M. F. of the magnitude of an arcing F. is a specialfeature of my invention. For cycle current and with transformer ironwhich will varry 60,000 lines per square inch in flux density, thesingle turn secondary voltage per. 100 square inches of core area wilLbeapproximately 15 volts, and for 80,000 lines about 20 volts. Thus if itis desired to induce. a single turn secondary voltage of 40 volts, atthe higher flux density, the core area necessary will be about 200square inches in cross sectional area. Lower voltages as may be requiredfor operation without arcing E. M. Fs. can be provided for by additionalturns on the primary and taps for different secondary voltages; ordifferent voltages may be applied to the primary winding.

Various details and forms of my invention are illustrated in the annexeddrawings in which Fig. 1 is a sectional elevation of one embodiment ofmy invention and Fig. 2 is a plan view in section of the furnace of Fig.1.

Fig. 3 is a sectional elevation view of a form of my invention wherein ahigh single turn secondary voltage is applied and where loose charge andscrap can be melted in accordance with my invention, and where moltenslag can be kept molten and heated by means of the high secondary E. M.F. I

Fig. 4 is a sectional elevation view thru the line AB of Fig. 3 andshows the slag bath heated by the hi h secondary single turn E. M. F.,indepen ently of electrodes.

I will now describe the different embodiments shown in these severaldrawings and the details therein.

Referring first to Figs. 1 and 2, there is shown in these figures aninduction furnace for melting and heating molten metal. This furnacecomprises a magnetic core 1 supported on the furnace frame work. It hasa primary winding shown diagrammatically at 2 by means of which arelatively high voltage may be induced in the secondary circuit formedby the annular channel 9. The core legs are shown in section at 3, 4 and5 in Fig. 2. A main chamber 7 is formed in the refractory lining 6. Aspout is shown at 8. One of the induction channels is indicated at 9.opening into the main her at 10. The connecting channel container 11holds the refractory material 15 inside of which is a resistor tube withthe hole 14 thru it. The connecting tube member joins with the mainchamber at 13 and with the opposite reservoir chamber at 12. Theinduction single turn channel is shown at 16 in the back part of thefurnace and a reservoir chamber 20 is indicated. in dotted lines above.The furnace is tiltable on a rocker 18. member 17 of material which willprotect the core from molten metal in case of a run out is shown. Thismay be transite asbestos wood. The insulating members between the metalshell 11 and the other parts of the furchamscrap I Th plete unbrokencircuit nace shell are indicated as at 19. A cover 21 is provided forthe reservoir chamber 20 and a cover 22 for the main chamber; The backpart of the furnace is removable. in place against the ends of the tubesby means of bolts 23 shown in Fig. 2 and a structural member 24. Thislatter may be removed in order to shown at connected to the rockers at25. An electrode 26 is shown entering the chamber 7.

The induction furnace shown in these Figs. land 2 operates either oncold charge to melt it or with molten metal. A core encircles each ofthe connector tubes 28 and 29. When the chamber of the furnace containsmetal which fills the connecting tubes, and current is applied to theprimary winding on the cores, current will flow thru the molten metalsingle turn secondary circuits. The amount of current will be regulatedby means of the voltage.

In order to start this furnace with cold may utilize the resistor tubesshown. ese may be made, for example, of graphite. If the furnace is usedto melt aluminum, for example, I may allow the metal to solidify in thegraphite tubes so that when the furnace is cold there is a metal circuitwithln the tubes and also a circuit around the cores of graphite. Therelative resistance of the graphite and the metal is regulated so as toprovide a considerable portion of the heat in the graphite proper, andto prevent too great a current in the alminum. In as much as the currentflows around the circuits thru the graphite, there does not need to be acomof aluminum. Thus the contraction of the aluminum when it freezes maybreak the circuit, but this will not prevent the operation of thefurnace because the current will flow thru the graphite.

The furnace chamber may be charged with cold scrap aluminum and theheating started. Aluminum scrap is also preferably charged into thechamber 20. As the graphite heats up the aluminum also heats and melts.The pressure of the metal in the outer chambers is preferably maintainedwell above the level of the top of the tubes, that is the top of thehole thru the graphite tubes. Thislessens the tendency to pinching.

The furnace may be rocked in any suitable my invention described in mycopending application for patent, Serial No. 455,601.

have shown the main chamber 7 constructed so that metal may be melted init by means of electrodes without entering the tubes, when this isdesired.

I have shown insulating members 19 between the ends of the tubecontainers and the shell of the furnace, thus preventing a circuitaround thru the furnace shell. These inv sulating members It is held getat the openings into the tubes- 27. A tilting mechanism may be may bethin mica or transite asbestos wood. 1

I have made the'straight tubes of silica with'a binder such as clay ormolasses water or silicate of soda. I have also used mixtures of fireclay and alumina.

magnesite and other refractories.

In repairing the inside of the tubes, I may remove the structuralmembers at the back of the furnace and place a pipe or bar inside thetubes and pour in refractory material or carbon paste around the pi e,allowin it to set and then withdrawing t e pipes an closing up theopening into the channel, as indicated at 27 in Fig. 2. I

Referring now to Figs. 3 and 4, I have shown in these illustrations amodification of my invention where a high single turn induced secondaryvoltage is advantageously applied for the melting of cold charge, eitherscrap or ore. Thus this form of my invention may serve to melt coldscrap metal charged into the chamber of the furnace, or the single turnvoltage may be applied so as to heat a slag bath into which the chargecomes and is smelted or heated.

The furnace consists of a frame 1 mounted on a rocker 2 and supports amagnetic core or cores indicated at 3'. The primary coil is shown at 4.The primary circuit is completed by means of the switch 5 and the sizeof the core and value of the primary supply voltage are selected to meetthe desired end and the value of the single turn secondary inducedvoltage is thus controlled.

The furnace has a main chamber 6 in refractory material and an auxiliaryor reservoir chamber 7 and connecting tubes as at 8. The metal in thesetubes and the chamber 7 forms part of the circuit and it is completed inthe chamber 6', either thru the scrap, or thru the scrap and theelectrodes 16 and 17'; or thru a slag bath indicated at 22'.

In the sectional view in Fig.4I have shown a water cooling member 24'having a water cavity 25' and inlet and outlet pipes 26 and 27' /forcooling water. This member serves to maintain the refractory bridgewhich separates the metal of the two ends of the secondary circuit. Thismember is shownat 13' in Fig. 3 and the top of the refractory isindicated at 14. The pipe leading from the water cooler member is shownin Fig. 3 at manner, as for example 1n,accordance with The electrodesshown diagrammatically at 16 and 17 may be used in a speciallyadvantageous way. They may serve to complete the sing e turn circuitthru the charge and I have shown a switch at 29 which may connect theseelectrodes either to a supply circuit iridependent of the furnace orfrom a windi on its core, or alternately to short they serve to carrythe circuitxthem so that curren from one side of the bridge of the Ihave also used alumina-slhca mixtures and also chrome,

hearth to the other side. These electrodes are shown relatively small indiameter, but they may be made relatively large sov as to coverquite anarea of the scrap charge. Thus in meltin cold. scrap where the circuitis completed from the metal in the tube by passing thru the scrap andback to the metal in tube 21', the current may pass thru the scrapindicated at 11 and pass directly from one side to the other, formingarcs as indicated at 19', or it may pass thru the scrap into theelectrode 16 and back thru the electrode 17, likewise forming arcs. Thevoltage of this circuit may be controlled as desired from a very lowvoltage up to as much as 300 volts which can be obtained with arelatively large magnetic core. When forming arcs thru the scrap as at19', the Water cooling member protects the hearth from wear and enablesit to withstand the high heat. However, I may operate this furnace andprocess by forming slag as a bath to connect between the metal at theends of the tubes 20' and 21'. Thus I may do what has not beenheretofore accomplished, namely, I may supply a relatively highvoltage-around the single turn circuit sufficient to cause the currentto flow thru a slag bath joining parts ofthe secondary circuit. And Ican do this without the use of electrodes. It is thus possible toprovide electric heat in a materially less expensive manner thanheretofore. This slag bath can be used for smelting purposes and thecharge can enter from above and drop on the slag bath and be heated andsmelted.

Scrap metal, and particularly volatile metal can likewise be thustreated. I

The tilting cylinder illustrated in the Fig. 3 comprises in reality twocylinders mounted with a single piston rod, and a piston in eachcylinder. The lower cylinder is for tilting the furnace and the uppercylinder is for giving it a limited rocking motion. The base of the maincylinder is shown at 37 and it is mounted on a pin to allow for themovement when tilting the furnace. The piston rod is shown at 40 with apiston 39 shown in dotted lines in the lower cylinder and another pistonon the other end of the same rod at 44 for operation within the uppercylinder, which latter is shown in section at 46, with its gland at 42.Inlet and outlet pipes for both cylinders are shown at 38, 41, 43 and45, and air or other fluid may be used, or water may be used. The uppercylinder is mounted on a pin 47 connected to the frame of the tiltingfurnace of Fig. 12. In operation this combination tilting apparatusserves to give a short movement to the shell by means of the doubleacting piston 44 and this move ment may be kept up mechanically as for9X: ample by means of a rotated 4-way 'valve which alternately appliespressure first to one side and then to the other of the piston 44. Thisvalve may be operated by a motor connect the piston or other means maybe used and the speed of reciprocation controlled. .When the inlet andoutlet pipes of the lower cylinder are both closed by suitable valves,the piston on the lower end of the piston rod can be held approximatelystationary and thus serve to directly with the base bearing as it were.On the other hand, when .it is desired to tilt the furnace for pouringits contents, the small cylinder operation can be stopped and thepressure admitted in the large cylinder to tilt the furnace over to thedesired extent.

The line C D in Fig. 3 illustrates the position of the top surface ofthe metal when the furnace is tilted so as to retain more metal in thechamber and to avoid short circuiting the secondary by a solid or moltenring of metal all the way around.

It is not necessary to maintain the metal in the induction tubes molten.The voltage may be sufficiently high and the current low enough so thatthis part of the circuit around the core, particularly away from themolten slag, may be below the solidifying temperature, and the metalwhich collects will then collect on either side of the refractory hearthbridge and not complete the single turn circuit. The furnace can ofcourse be operated without rocking it, and the conductor metal in thetubes may even be kept solid by water cooling, when desired, or bysimple radiation. It is understood that altho I have shown thisimprovement in a certain shape of furnace, my invention is by no meanslimited v to that kind of a furnace, but the induction circuits may beapplied from the bottom or side or end and the main hearth may be ofsuch shape as will most easily suit the process under operation.

Where I use a separate magnetic circuit around different parts of thesame single turn secondary circuit, it is understood that I may providea separate primary coil on each core member and these two coils may beinterconnected electrically so as to operate either in series or inparallel across the supply line voltage, and thus serve as a means ofsecondary induced voltage control independently of taps on those coils,which also may be used.

In the construction of furnace illustrated in Figs. 1 and 2, I mayhold'the two main chambers together by any suitable pressure means, suchas the bolts 23. When a. new tube is to be put in place, the pressure isreleased so as to' lift, away the back chamber or either of them, as forexample by means of a crane and hooks on the furnace shell. The boltsthru the insulating members like that shown at 19 in Fig. 1, areloosened to release this is squeezed out away from the hole thru thetube when it is pressed between the two chambers. When this is done, itis preferable to have a bar of pipe inside the hole to prevent theplastic material closing the hole.

I may, however, repair the inside of the tubes without removing themfrom their position between the chambers by placing inside the hole inthe refractory a pipe or bar the size the hole should be and tilting thefurnace and pouring into the opening between the pipe and the refractoryfluid mud or fluid with mud of refractory nature in suspension so thatit fills up the space which has been corroded.

The magnetic core of Fig. 2 is preferably made in two separate parts andeach part has its separate primary coil as indicated at 2. The preferredlocation of these coils is above the tubes. Then in event of a run outthe coil is not damaged by molten metal.

The electrode shown in dotted line in Fig. 1 illustrates how the furnacemay be operated in case it is desired to heat the metal with electrodecurrent with the furnace tilted over so that the metal is not in thetubes.

In the modification Where a carbon resistor tube is used I may make aconstricted portion of small diameter in the tubes to limit the currentin the metal contained.

It is important to provide a sufficient magnetic core area to permit therelatively high single turn secondary E. M. F. necessary for carryingout my invention. As mentioned the core may be of suflicient fluxcapacity to induce a single turn voltage of as much as 300 volts. Whereit is desired to utilize induction heating by means of high secondaryinduced E. F. and to heat a circuit including molten slag or unreducedmaterial as well as molten metal, voltages of 50 to volts across themolten slag portion of the secondary may be used. This induced voltagemay be regulated, adjusted and controlled by means described in myPatent No. 1,662,149

of March 13, 1928, either without stopping the flow of secondary currentor by change of taps with the current stopped.

It is understood that the cross sectional shape of the secondarychannels may be other than round, and that the various combinationsdescribed herein may be further modified without getting away from theinvention.

Altho I have shown'in Fig. 1 a furnace in which solid tubular resistorsare included, it is to be understood that the straight channel sectionsthere illustrated may be made of refractory material without the hollowresistors.

What I claim is:

1. Anelectric induction heating furnace comprising a heat refractoryfurnace body having a chamber for a charge, an annular channel of smallcross-section communicating with the chamber forming a closed secondarycircuit and permitting the passage of the molten charge therethrough, aprimary coil associated coil and secondary circuit being so constructedand arranged that a relatively high voltage is induced in said secondarycircuit.

2. An electric induction furnace comprising heat refractory furnace bodyhaving a chamber for a charge of loose scrap electro conductivematerial, an annular channel of relatively small cross-section, saidchannel forming a closed secondary circuit and permitting the passage ofthe molten charge therethrough, a primary coil associated with saidsecondary circuit the coil and secondary circuit being so constructedand arranged that a voltage of sutficient magnitude to cause arcingbetween the individual particles of the charge is induced in saidsecondary circuit.

3. An electric induction furnace comprising heat refractory furnace bodyhaving a chamber for a charge, an annular channel of relatively smallcross-section communicating with the chamber said channel forming aclosed secondary circuit and permitting the passage of the molten chargetherethrou-gh, and a primary coil associated with said secondary circuitand arranged to induce a relatively high voltage in the secondarycircuit. said chamber being provided with a low partitioning bridge fornormally projecting into the stream of the molten charge.

In testimony whereof, I hereunto subscribe my name this 22nd day ofNovember, A. D. 1928.

ALBERT E. GREENE.

with said secondary circuit, the

